1. Field of the Invention
This invention relates to carbon fiber-reinforced light metal composites, i.e. carbon fibers bound with aluminum or aluminum alloy (hereinafter referred to collectively as "aluminum metal") or magnesium or magnesium alloy (hereinafter referred to collectively as "magnesium metal).
2. Discussion of the Background
The aluminum metal or magnesium metal containing carbon fibers are generally designated as carbon fiber-light metal composites or carbon fiber-reinforced light metals. As a light weight structural material possessing higher heat resistance than carbon fiber reinforced plastic (CFRP), the carbon fiber-reinforced light metals have been the subject of research devoted to development of applications in various industrial fields, typically the aerospace industry. Carbon fibers, however, are not readily wetted with the molten light metals aforementioned. When the carbon fiber-reinforced light metal is to be produced by a molten metal impregnation method, therefore, the carbon fibers are required to be covered with a coating which is readily wettable with the molten light metal. As a material for such a coating, a titanium-boron intermetallic compound has been known to the art (Japanese Patent Public Disclosure No. SHO 51(1976)-81703), but the observed values of the strength of aluminum metal or magnesium metal composites reinforced with carbon fibers coated with a thin layer of the titanium-boron intermetallic compound are considerably lower than the theoretical value based on the rule-of-mixtures. Such a deterioration is more remarkable for the carbon fibers produced at a temperature below about 1500 .degree. C. than for the fibers produced at a higher temperature. This deterioration is due to the occurrence of reaction of the carbon fibers with such a metal. Since the Ti-B coating has little effect for protecting the carbon fiber from the reaction, more improved coatings are desired to be developed.